1. Field of the Invention
The present invention relates to a radio-thermometer system. More particularly, the present invention relates to a radio-thermometer system and method for measuring electromagnetic energy radiated from an interior of a human body using the same.
2. Description of the Related Art
Ordinary objects emit electromagnetic energy in a predetermined frequency band at an absolute temperature of 0° K. or higher. Some objects, however, completely absorb energy around them and emit electromagnetic energy in nearly all frequency bands. These objects are called black bodies and radiate energy according to Plank's radiation law, which will be explained in connection with a graph shown in FIG. 1.
FIG. 1 illustrates a variation of an intensity of radiant energy of a black body with respect to frequency. Referring to FIG. 1, the intensity of radiant energy of a black body varies from frequency to frequency and peaks in the infrared range, i.e., between 3–15 μm. Generally, radiant energy of a black body in the infrared range can be detected using an infrared camera, while radiant energy of the black body in a microwave range can be detected using a radio-thermometer having a directional antenna and a high sensitivity receiver. Radio-thermometers, which were first adopted in the field of astronomy, have been used primarily for measuring energy radiated from planets or stars in the universe and estimating the temperatures of those planets or stars.
Given that in the infrared range, human skin exhibits almost the same energy characteristics as a black body, a distribution of temperatures on the surface of the human body can be obtained by measuring energy radiating from the human skin in the infrared range. Recently, radio-thermometers have been increasingly used for receiving energy from tissue within the human body and for measuring a temperature of those tissues.
Human skin, however, does not act as a black body in a microwave frequency range. Thus, not all of the electromagnetic energy radiated from inner tissues within the human body is transmitted to the surface, i.e., the skin. The intensity of the electromagnetic energy transmitted from the inner tissues of the body to the skin may vary depending on through which medium, e.g., muscle, bone, or fat, the electromagnetic energy travels between the tissue and the skin. Radio-thermometers using microwaves estimate an internal temperature of a human body by measuring electromagnetic energy radiated from the human body having a frequency of 1 GHz–6 GHz at the surface, i.e., the skin, of the body.
FIG. 2 is a diagram illustrating a conventional radio-thermometer system 20 using microwaves. Referring to FIG. 2, a signal output from a noise source 9, which is controllable, is input to a first attenuator 10, which is adjustable, and then to a directional coupler 13, which is connected, via an antenna 4, to a target object 1 having a temperature to be measured. The signal output from the controllable noise source 9 is also input to a second attenuator 11, which is adjustable, and then to a first terminal of a switch 2. A second terminal of the switch 2 receives energy emitted from the target object 1 and energy reflected from the target object 1. The switch 2 is periodically switched by a clock pulse generator in a radio-thermometer 8. A signal output from the radio-thermometer 8 is provided to an output terminal, via an integrator 14, as a voltage Ua corresponding to a temperature To of the target object 1. The conventional radio-thermometer system 20 measures an internal temperature of the target object 1 by adjusting the noise source 9 several times.
Difficulties in obtaining an accurate internal temperature measurement by the conventional radio-thermometer system 20 may be caused by interference of electromagnetic waves in and around the conventional radio-thermometer system 20 or by an impedance mismatch at an interface between the antenna 4 and the target object 1. The problem of the interference of electromagnetic waves can be solved by taking measurements in an electromagnetic wave shielded room. However, the problem of impedance mismatch at the interface between the antenna 4 and the target object 1 remains responsible for a lack of reproducibility and thus causes errors in the measurement.
Therefore, it is necessary to develop a new radio-thermometer system that is able to precisely measure the temperature of the target object 1 even though an impedance mismatch occurs at the interface between the antenna 4 and the target object 1.